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  <div class="titlepage"><div><div><h1 style="clear: both">Phase 3</h1></div></div></div>
  <p>We have built our first two phases of construction for <code>file_handle</code>,
and for some users they might be happy writing:</p>

<div class="code-snippet"><div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++">  <span class="n">outcome</span><span class="o">::</span><span class="n">result</span><span class="o">&lt;</span><span class="n">file_handle</span><span class="o">&gt;</span> <span class="n">fh1</span> <span class="o">=</span> <span class="n">file_handle</span><span class="o">::</span><span class="n">file</span><span class="p">(</span><span class="s">&#34;hello&#34;</span> <span class="cm">/*, file_handle::mode::read */</span><span class="p">);</span>
  <span class="k">if</span><span class="p">(</span><span class="o">!</span><span class="n">fh1</span><span class="p">)</span>
  <span class="p">{</span>
    <span class="n">std</span><span class="o">::</span><span class="n">cerr</span> <span class="o">&lt;&lt;</span> <span class="s">&#34;Opening file &#39;hello&#39; failed with &#34;</span> <span class="o">&lt;&lt;</span> <span class="n">fh1</span><span class="p">.</span><span class="n">error</span><span class="p">().</span><span class="n">message</span><span class="p">()</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
  <span class="p">}</span>
</code></pre></div><a href="https://github.com/boostorg/outcome/tree/master/doc/src/snippets/constructors.cpp#L185" class="code-snippet-url" target="_blank">View this code on Github</a></div>


<p>&hellip; and be done with it.</p>

<p>But wouldn&rsquo;t it be nicer if we could instead write:</p>

<div class="code-snippet"><div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++">  <span class="n">outcome</span><span class="o">::</span><span class="n">result</span><span class="o">&lt;</span><span class="n">file_handle</span><span class="o">&gt;</span> <span class="n">fh2</span> <span class="o">=</span> <span class="n">make</span><span class="o">&lt;</span><span class="n">file_handle</span><span class="o">&gt;</span><span class="p">{</span><span class="s">&#34;hello&#34;</span> <span class="cm">/*, file_handle::mode::read */</span><span class="p">}();</span>
  <span class="k">if</span><span class="p">(</span><span class="o">!</span><span class="n">fh2</span><span class="p">)</span>
  <span class="p">{</span>
    <span class="n">std</span><span class="o">::</span><span class="n">cerr</span> <span class="o">&lt;&lt;</span> <span class="s">&#34;Opening file &#39;hello&#39; failed with &#34;</span> <span class="o">&lt;&lt;</span> <span class="n">fh2</span><span class="p">.</span><span class="n">error</span><span class="p">().</span><span class="n">message</span><span class="p">()</span> <span class="o">&lt;&lt;</span> <span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
  <span class="p">}</span>
</code></pre></div><a href="https://github.com/boostorg/outcome/tree/master/doc/src/snippets/constructors.cpp#L192" class="code-snippet-url" target="_blank">View this code on Github</a></div>


<p>The eye is immediately drawn to the two-stage invocation pattern, so we are
constructing a type <code>make&lt;file_handle&gt;</code> using the arguments with which we wish
to invoke the <code>file_handle</code> constructor with, and then invoking the
call operator on that <code>make&lt;file_handle&gt;</code> instance to do the
actual construction.</p>

<p>It may seem a bit clunky to use brace initialisation for parameters followed
by a &ldquo;spurious&rdquo; set of empty brackets, but we think that this is a better
approach than alternatives. We shall briefly cover those at the end of this section.</p>


        </div><p><small>Last revised: February 08, 2019 at 22:18:08 UTC</small></p>
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